1. Field of the Invention
The present invention relates to an iris recognition system. In particular, the present invention relates to a display device of a focal angle and distance in an iris recognition system, which enables to focus a camera to obtain more accurate iris images, measure a focus angle and distance between the camera and a user, and using the measurement result, to instruct the user which direction and how far he should go with respect to the camera.
2. Description of the Related Art
As well known already, there have been a number of systems for security, crime prevention, and identity authentication, such as the traditional contact cards system or the non-contact cards system and up to the fingerprint recognition system. The iris recognition system has certainly joined this stream for authenticating a person's identity before allowing or rejecting the person to enter a particular place or to access specific data.
Among those, the iris recognition system is considered to be the best for its high recognition rate compared with the fingerprint recognition, and for its high accuracy. The iris recognition system is a technique for authenticating a person by comparing a pre-registered iris data with a new iris data that has been prepared by capturing iris images using a video camera and making iris pattern features into data using an image process technique.
FIG. 1 is a schematic diagram of a general iris recognition system in a related art. With reference to FIG. 1, operation of the iris recognition system is now explained below.
As a user approaches the iris recognition system, a distance measurement sensor 109 measures the distance between the user to the system, and a controller 105, having received the distance measurement value through an actuator 107, decides whether the distance measurement value is within the operation limit.
If it turns out that the user is within the operation limit, a control signal is sent out to the actuator 107 to extract iris images. And, the actuator 107 sends an active signal to an external indicator 108 and lets the user know that the system is on. When the user puts his or her eyes on an optical axis of a camera 103 through an optical window 101, a cold mirror 102 blocks a visible ray and passes infrared rays. And, the system indicates whether the iris of the user should be placed to make sure the user's eyes are properly positioned on the optical axis of the camera 103.
The control device 105, on the other hand, is provided with the distance from the distance measurement sensor 109 to the user, and based on the distance measurement value, it calculates zoom and focus values of the camera 103 and performs zoom in/zoom out and focusing control. Later, the control device 105 adjusts the intensity of an illumination device 106 through the actuator 107 in accordance with the distance measurement value, and photographs the iris image using the camera 103. The photographed iris image goes through a signal process to be appropriate for the iris image analysis at a frame grabber 104, and based on the information about the processed iris image, the control device 105 recognizes the iris and decides whether or not to authenticate the user.
The performance of this iris recognition system is totally dependent on how fast and how accurately it can recognize the iris.
There are different kinds of techniques of extracting the iris image in order to photograph the iris of the user from an appropriate distance. For example, sometimes the user himself has to focus the camera by looking at the screen and moving back and forth, or in some cases, several cameras are used at one time to find out where the user's face and eyes are and photograph the user's iris image. Also, some obtain the iris image by using the distance measurement sensor which measures the distance between the camera and the user in order to focus the camera automatically.
First of all, it would be pointless to say that the user would feel uncomfortable if he personally has to move around within a certain distance to focus the camera, while looking at the screen. Also, in this case, a single light source is used. Therefore, if the user wears glasses, the reflected image from the glasses makes it difficult to catch more accurate iris images. However, to prevent such problem, the user should keep moving while looking at the screen for himself until no reflection occurs, increasing inconvenience to the user.
Fortunately, using several cameras to focus the camera and obtain iris images has somewhat solved the trouble the user had to go through. But this time, the equipment is very complicated for a normal person to operate and it required very sophisticated control. In other words, the system uses two cameras for finding out where the user's face and eyes are, and another camera for obtaining the iris image. Although the system is convenient to use in that the user does not have to focus his eyes personally for the iris recognition because the system automatically focuses the camera and catches the iris image, the system configuration itself is very complicated in order to use several cameras and operate each camera systematically and electrically,
Lastly, in case the distance measurement sensor is used to focus the camera and photograph iris images, the distance measurement sensor senses a person's approach and focuses the camera based on the inputted images in possession and the focus values outputted from the camera.
However, since this technique also uses a single light source, the reflection problem due to the glasses of the user is likely to happen any time. As an attempt to avoid the secondary reflex due to the glassed, three LED (light-emitting diode) illuminations were put on the left side, the right side, and the upper side. But it was still uncomfortable to use because one should keep changing positions of the illuminations to get the images.
FIG. 2 is a block diagram of an autofocus adjusting device using a distance measurement sensor.
As shown in the drawing, a distance measurer 202 measures the distance between the user and the camera 205 at designated regular time intervals using the distance measurement sensor 201, and outputs the distance information successively. A distance processor 203, using the distance information, catches characteristics of the user's movement. More specifically, based on that successive distance information, the distance processor 203 measures the user's movement speed. If the speed is a positive number (+), it means that the user is approaching, and if the speed is a negative number (−), it means the user is going away, and if the absolute speed is within the limit, it means the user stopped moving.
A camera operation controller 204, using the information about distance, speed and acceleration provided from the distance processor 203, controls the operation of the camera 205 when the use stands still. Here, even when the user's movement is not yet stabilized, it is important to estimate beforehand where the user is going stop and drive the camera's lens to that position because it certainly reduces time necessary for focusing the camera.
When the user's movement is stabilized, the camera operation controller 204 adjusts the camera's zoom and focus based on the distance measurement values. Considering that the user can't be perfectly still but keeps moving little bit and the measured distance values are not necessarily the actual distances to the user's eyes, it is rather natural to accept the possibility of measurement error to a certain degree. Therefore, a fine adjustment process is carried out involving the camera operation controller 204, in which the camera operation controller focuses the camera by analyzing the successively inputted iris image from an image controller 206, calculating a focus range therefrom, moving a zoom and focus lens until the focus range becomes appropriate for performing authentication, and continuing the tracking until a maximum value is obtained.
However, if the user is wearing glasses, the iris image of the user could be reflected in accordance with the angle between the glasses and the LED mounted at an illuminator 208. To prevent this problem, the image processor 206 detects a possible reflection degree before calculating the focus range, and outputs the glasses reflection information to an illumination controller 207.
In a way of avoiding the glasses' reflection, the illumination controller 207 controls the lighting condition of the illumination LED based on the glasses reflection information, and changes the reflected positions from the glasses as well. In this manner, the reflection by the glasses can be prevented and the iris image recognition can be done successfully through an analysis on the iris images obtained from the camera 206.
However, one problem of the system is that it depends too heavily on the distance measurement sensor to measure the motion direction and distance of the lens when the camera needs to be focused. Thus, if the distance measurement sensor does not give accurate information on the distance to the user's eyes, which unfortunately does occur very often, the motion direction of the lens could be designated to a wrong direction and the time for adjusting the focus might take longer than expected. In addition, since the user has to approach within the permitted limit of the iris recognition system, the system is not that convenient for the user.
On the other hand, a combination camera for a video conference and iris recognition, which combined a camera for a video conference and an iris recognition camera into one system, has been introduced for recognizing an iris for an equipment like a personal computer system.
FIG. 3 is a diagram explaining a relation between the combination camera and the user in terms of position and distance.
As depicted in the drawing, the iris recognition system requires the user to adjust the focal distance (D) and the focal angle accurately while watching the combination camera for a video conference and iris recognition to get desired iris images.
In other words, the focal angle means the operation limit of X-axis and Y-axis between the user and the iris recognition camera, and the focal distance means the operation limit of Z-axis between the user and the iris recognition camera.
According to the system shown in FIG. 4, the user is supposed to put his eyes on the place where the distance and the focus adjusting image in the iris recognition camera with a single focus lens (use two circles with different colors) conform to each other. In short, the system does not start iris recognition until the user looks at the place where two points in the camera converge.
For a better adjustment of the focus position, the user is recommended to keep a certain distance from the camera (i.e., 44 cm to 48 cm), and is encouraged to adjust the focal angle using a blue circle and a white circle in the camera lens. In other words, the user is supposed to keep looking at the camera and move towards where he can adjust the focal angle until the two circles become one.
FIG. 4(a) illustrates a case where the focal angle is adjusted and (b) illustrates a case where the focal angle went wrong.
FIG. 5 illustrates an internal configuration of an optical system for leading and guiding the user to adjust the focal angle in the combination camera for a video conference and for iris recognition in the prior art.
Referring to FIG. 5, the optical system includes an iris recognition camera lens 301, a reflection mirror 302 for sending eye images of the user that are incidented through the lens, and an iris recognition camera 303. Moreover, as shown in FIG. 4, a light emitting diode (LED) 304 for making two circles and displaying them is mounted on a back surface of the reflection mirror 302, and a circular hole 302a is formed on the reflection mirror 302 for transmitting the LED 304 light.
In this manner, the LED 304 light transmits the lens 301 through the hole 302a, and the user can see the circular light with a designated color and adjust the focal angle by moving the lens 301 right and left and up and down, until the circle with different color and size on the lens matches with the circle by the LED.
However, this device strongly encourages the user to practice to get the feeling of the focus position beforehand using a tapeline or something until he becomes intuitively accustomed to the focus position to a certain level. But for the user, it is rather difficult and inconvenient to adjust the focus position, making the white circle out of those two circles looking in the camera lens become one with the blue circle at the same time. Considering the small sized lens and visual difference of the user's eyes, the task seems to be even harder.
Moreover, because the system uses two lenses and the distance between the LED and the lens is very short, the user, even when he is not at the right front of the lens, could see the LED light, so he cannot be sure whether the focal angle is properly adjusted or not. Further, there is a white point marked on the surface of the lens such that the user can see the LED light from any angle and focus, but this can be an obstacle to obtain good iris images. On top of boring a hole in the reflex mirror to transmit the LED light, if the user looks at the iris recognition camera from a different angle rather than the front, it is very hard to adjust the focal angle since the camera would not look like a circle to the user then.